Revert BEGIN work, as it breaks Rakudo.

It now lives in a branch begin-lexicals.
Revert routine wrapping; breaks Rakudo build.

This commit can also be found in begin-lexicals branch now.
Invoke accepts_type on correct meta-object.
Be sure to keep tc.curFrame in sync.
Handle arity-1 loop constructs.
nqp::decont shouldn't explode on nulls.
Make CallCapture REPR clonable.
special-case negative values in rshift

... and treat rshifting by an negative amount like an lshift by
positive amount.
Add a JavaWrap representation and associated code
stub jvmbootinterop access